Failsafe logic circuit wherein the phototransistor of a preceding optocoupler is connected in series with the photodiode of a succeeding optocoupler

Claim 1

Failsaft AND or NOR logic circuit comprising: a combinatorial logic circuit having at least one signal input and only one ultimate signal output, said combinatorial logic circuit including optocouplers as coupling elements by which said at least one signal input of said combinatorial logic circuit is connected with said ultimate signal output according to the implemented logic circuit; an alternating voltage source connected to said combinatorial logic circuit to activate the combinatorial logic circuit according to said alternating voltage; and an AC signal conductive component responsive to said alternating voltage and connected to the output of said combinatorial logic circuit for passing only alternating current signals; wherein one optocoupler is provided per signal input whereat the signal inputs of said combinatorial logic circuit are applied to the cathodes or anodes of photodiodes of said optocouplers, each said optocoupler having a single transmitter and a single receiver and being unrestricted as to control frequency of timed input pulses; wherein said optocouplers are arranged in a series circuit with the phototransistor of a preceding optocoupler being in a series connection with the photodiode of a succeeding optocoupler; and wherein the photodiode of the first optocoupler is fed by the alternating voltage of said alternating voltage source and the phototransistor of the last optocoupler provides the ultimate signal output of the combinatorial logic.